Sick of the east wind? Is La Niña a bust already? Worried about (the lack of) mountain snow?
The answers to these questions are related. Let me first give the short answers and then elaborate.
The east winds will weaken and strengthen, but in our current pattern. They're not likely to completely go away for a while.
La Niña lives on.
As far as the mountain snow, I’m not worried. A couple weeks of dry weather does not doom a season.
That premise leads me into the big picture. It’s easy to forget, but important to remember that seasonal forecasts, like the forecast for our current La Niña winter to bring ample Cascade snow, are forecasts for an entire season. It means at the end of March, we’re likely going to have above average snowpack. It doesn’t mean there will be no dry stretches on the way there.
La Niña is interesting because in one sense it’s a pattern that is out of phase with climate normals. That means during a La Niña there are areas of warm air aloft (high pressure), where long term average shows cold air aloft (low pressure) should reside, for example. One such place is the North Pacific. Above is a map of typical jet stream and weather patterns during a La Niña winter.
See that giant “H”, blocking high pressure, south of Alaska? This is in the same general area where the Aleutian Low generally hangs out in a No Niño winter. That’s what I mean about out of phase with normal climate patterns.
OK, so what? Well, a couple things:
It means that over the Northwest, there’s often a jet stream coming from the NW, or even straight from the north. That’s the cold part. But a shift in exactly where that jet stream is can result in cold and wet weather, or, like we’ve had for the first part of this December, cold and dry weather. So I’m not surprised we’re seeing this long dry period right now. Big picture, in terms of the weather pattern across the northern hemisphere, is it’s not out of line with what I expect in a La Niña year. It’s just shifted the jet stream a bit east right now, which pushes storms to our east. When the pattern changes again, it’s easy to envision a series of cold storms dropping in with abundant mountain snow. It’s also not a reach to see it shift in a way that allows Arctic air to drop down over and west of the Rockies. That’s often a set up to valley snow west of the Cascades. I don’t see that happening before the New Year, so don’t get too excited about a white Christmas.
Back to the out-of-phase theme. Ever hold a beach ball under water in a pool or lake? You can do it for a while, but then some shift in your weight, or a wave, or some kid doing a cannon ball off the diving board, throws you off and the ball pops to the surface. The ball is back to its normal place. You’re the La Niña force trying to keep the ball under water and out of phase from normal. Left on its own, the ball prefers to float on the surface.
The atmosphere also prefers to be close to climatic normals, That’s how the positions of highs and lows get to the esteemed title of “climatic normals”. So in a La Niña pattern, there’s a battle going on between the forces of La Nina, and the forces of normal. And probably other forces, like climate change, whose impacts on seasonal weather patterns are less understood. But it all leads to a lot of back-and-forth between normal and more extreme weather. And that means a lot of variability in our winter weather. We've seen this already this fall. Remember November? Very wet, a lot of mountain snow in the middle of the month. Then suddenly December has been dry and warm in the mountains. Variability on display.
So to answer the “Is this La Niña a pattern a bust?” question, no, the pattern isn’t a bust. The pattern persists and is likely to continue. But it’s not that simple. Forecasting rarely is. Here’s the thing: Not every La Niña is the same. Other forces are at work, and there are differences among La Niñas in the distribution of tropical Pacific sea surface temperatures that define La Niña in the first place. So while La Niña exists, the parade of storms we come to expect can easily come and go.
So, what about Cascade snow? It’ll come. In La Niña I trust. And the second year of back-to-back La Niñas, which this is, usually produce.
Keep in mind, east winds, varying in strength, is the norm this time of year. Northerly jet streams can be common in La Niña years. Those can deliver a lot of high pressure east of the Cascades. Hello east wind. It’s likely to be interrupted as the pattern shifts and storms arrive. But this current pattern keeps the east wind going through the week.
We’ll get the monthly La Niña update from the good folks at the Climate Prediction Center at the end of the week. We’ll see how she’s doing then and what that may mean for our winter.
In the meantime, enjoy the bubble of December sun!